SALT LAKE CITY — The progressive activists who gathered in Utah two weeks ago to strategize for the midterm elections could each recall a moment when they realized the Democratic Party was their foe and decided to quit it.

For Kenneth Mejia, 27, who ran for Congress as a Democratic write-in candidate two years ago, it happened when the party declined to include policies that inspire him — like single payer health care and a ban on fracking — in its 2016 party platform.

For Diane Moxley, 49, who canvassed for Barack Obama in 2008, it waswhen the Occupy Wall Street movement introduced her to others who shared her unease with the party’s acceptance of corporate donor money.

And for Rodolfo Cortes Barragan, 30, who wept when Al Gore lost the 2000 election, the moment came when Bernie Sanders endorsed Hillary Clinton for president at the Democratic National Convention in Philadelphia. It is an event he calls “the Wells Fargo Center incident,” named for the convention’s location.

Green party candidates took photos at the party's annual national meeting in Salt Lake City in mid-July. Party leaders said they expected to field at least 224 candidates for a variety of offices in 32 states this year.CreditKim Raff for The New York Times

Diane Moxley is running for Congress in New Jersey’s Seventh District.CreditKim Raff for The New York Times

Kenneth Mejia is running for Congress in California’s 34th District.CreditKim Raff for The New York Times

All three are now members of the Green Party, the leftists often accused of spoiling presidential elections for the Democrats. Each of them is now running for Congress in a year when young liberal activists have energized the Democratic Party, which increasingly echoes Green Party goals on issues like health care and campaign finance. But the Greens want no part of Democratic Party’s ascendant left wing: As much as they may loathe President Trump, they say several issues — including corporate donations and support for capitalism — have rendered both the Democrats and the Republican Party rotten to the core.

“Regular working people, families, are not being represented by the government in Washington right now,” said Mr. Cortes Barragan, a psychologist who is living with his parents while he pays off $40,000 in student loans. “That is because the Democratic Party followed the Republican Party in aligning itself with corporate America.”

A wave of liberal excitement has raised hopes for a “blue wave” in the midterms and empowered a new crop of progressive Democrats, like the democratic socialist Alexandria Ocasio-Cortez. But it has also paid dividends for the Green Party, whose formal endorsement of anticapitalism in 2016 helped set them apart from the Democrats and contributed to a swell of new members, many of them young people and ex-Democrats embittered by Mr. Sanders’ primary loss.

The Greens find themselves looking optimistically toward the 2020 presidential election, but it is unclear who their standard-bearer would be. Jill Stein, the party’s nominee in 2012 and 2016, said in an interview that she would like to see the party cultivate new leaders.

“Three times is a lot. It’s a lot for any one person and it’s a lot for a party,” she said. “I would be kind of shocked if it came to that.”

But she remains widely popular among party activists, despite suspicion expressed by the chairman of the Senate Intelligence Committee over her relationship to Russia, which she rejects.

“This is a generation that has been so badly burned and sees their future so bleak right now that they’re not terribly forgiving,” she said. “They really see Democrats as having misled them.”

Jill Stein said she has no plans to run for president a third time despite her popularity among Green Party activists.CreditKim Raff for The New York Times

Party leaders say there are now over 255,000 registered Greens in the 21 states, plus the District of Columbia, that give voters the option to register with the party, an increase from 216,000 in July 2016.

Their growth is due not just to the failure of Mr. Sanders campaign, but to what many Greens see as the success of Ms. Stein’s, which raised three times as much money, $3.4 million, and got over three times as many votes as she did in 2012. She appeared on the ballot in 45 states, the most ever for a Green nominee, and won over 1.4 million votes, or roughly one percent.

Last month, 175 Green Party activists from more than 40 states gathered at the University of Utah for their annual conference, where they dined on pizza alongside students in the cafeteria, placed bids on secondhand sci-fi books and homemade wine at a silent auction, and discussed their dream of implementing eco-socialism and ranked choice voting.

But the most pressing matter was the midterm elections, which for them are an important first step in the 2020 presidential campaign. Under the state-by-state patchwork of ballot access laws, Green candidates need to win enough votes in November, generally between one and five percent, to secure a spot on the presidential ballot in most states.

Jon Mann wore a jacket covered in political buttons to the annual Green Party meeting.CreditKim Raff for The New York Times

David Young Ho Kim wore a hat with a play on President Trump’s “Make America Great Again” campaign slogan.CreditKim Raff for The New York Times

Party leaders said they expected to field at least 224 candidates for a variety of offices in 32 states this year. There are already 155 elected officials nationwide who are Greens, most of them serving in local offices like city councils or on school boards.

But because the party does not accept money from corporations, unions or political action committees it has never won the kind of race that takes deep pockets, like governor or anything at the federal level. There is no indication that is about to change.

But that has not deterred candidates like Mr. Mejia, Mr. Cortes Barragan and Ms. Moxley, who are running for Congress armed with little more than shoestring budgets and the strength of their convictions.

Mr. Mejia and Mr. Cortes Barragan will face off against Democratic incumbents in Los Angeles, Rep. Jimmy Gomez and Rep. Lucille Roybal-Allard (Mr. Mejia advanced after defeating a Libertarian Party candidate, Angela McArdle, in the state’s top-two primary system.) Ms. Moxley is running in New Jersey against Leonard Lance, the Republican incumbent, and a former Obama official, Tom Malinowski.

“Regular working people, families, are not being represented by the government in Washington right now,” said Rodolfo Cortes Barragan, center, who is running for Congress in California's 40th District.CreditKim Raff for The New York Times

As far as New Jersey is concerned, Ms. Moxley said she thought “there really is no difference now” between the Democrats and the Republicans. That sentiment is not shared by Democrats and Republicans, but at the Green Party convention Ms. Moxley was not alone in that belief.

Even in the age of President Trump — whom they concede may be uniquely hostile to their principles — there are many Greens who squint to see the difference between the Democratic and Republican parties.

“They are not different enough to save your job, to save the climate, to save the economy and to save the peace,” said Ms. Stein. “The reality is we are going further and further over the edge here, whether it is a Democrat or a Republican, and it’s not as if Hillary would have stopped this slide into catastrophe.”

The Democratic Party loomed large over the Green conference, where attendees ruminated over the many ways they claimed the Democrats had slighted or sabotaged them over the years.

There was the ongoing legal challenge mounted by Democrats in April to remove the Green Party from the ballot in Montana, where a vulnerable Democratic senator, Jon Tester, is seeking re-election in a state President Trump won by 20 points.

And last November, the Senate Intelligence Committee requested documents from the Stein campaign as part of its investigation into Russian interference in the election.

Greens viewed the request as a political smear. The campaign submitted some documents in March but withheld others, citing the First Amendment. Ms. Stein said they had received no follow-up questions from the committee.

Ms. Stein also blames “Democratic operatives” for years of unfavorable coverage in the news media. And, of course, there is the word that irks the Greens more than any other: “spoiler.”

The Greens have been accused of dividing the left and helping Republicans win elections ever since Ralph Nader, the party’s 2000 presidential candidate, won 97,488 votes in Florida, where George W. Bush beat Al Gore by just 537 votes.

Hillary Clinton repeated the allegation in her campaign memoir, where she said Ms. Stein’s vote tally in Michigan, Pennsylvania and Wisconsin — states she lost to President Trump — helped doom her campaign, which lost the Electoral College but won the popular vote.

Attendees cheered the kick off of the Green Party's national meeting in Salt Lake City in mid-July.CreditKim Raff for The New York Times

Greens bristle at the “spoiler” accusation, which they say ignores poll data that suggested many of Ms. Stein’s 2016 supporters either would not have voted if she had not been on the ballot or would have voted for Mr. Trump.

“Candidates have to earn votes, they don’t own votes,” Ms. Stein said. “That in a nutshell is the problem with the Democrats, it’s the arrogance of thinking they own the system.”

While the Green Party and the progressive wing of the Democratic Party share a great deal of common ground, the Greens express a mix of grand idealism and grim cynicism: they believe American society is capable of revolutionary change, but the Democratic Party is not.

Gloria Mattera, one of the party’s co-chairpersons, said she doubted that the enthusiasm currently propelling the Democratic Party’s left flank would lead to a lasting change in its priorities.

“I don’t think one or two wins around the country in a Democratic primary should be dismissed, but they’re not a revolution inside the party, either,” said Ms. Mattera. “The Democrats will eat their own young, if you ask me.”

Attendees recorded segments for a campaign video for the Green Party during the annual meeting.CreditKim Raff for The New York Times

Liam Stack is a political reporter. Before joining the politics team, he was a general assignment reporter based in New York and a Middle East correspondent based in Cairo. @liamstack

A version of this article appears in print on Aug. 2, 2018, on Page A18 of the New York edition with the headline: Green Party, With an Eye on 2020, Prepares for the Midterms